I've got a problem with frost building up outside the intake duct for the exchanger. It is insulated and still sweats. I will be covering the walls with drywall and need to remedy this issue. Is this caused by to long of an exchange? What to do? Thanks!

So you mean the duct running from the outside intake to the exchanger inside the house right?

I had this issue in our last house. I ended up going with a higher R value (R8 I believe) flex duct on this house and haven’t had an issue yet. I think the "stock" insulated flex duct is R4? and then you get condensation inside it and it get the insulation wet and the situation gets worse. I wish they made a R16 or more flex duct to avoid this, but I would be curious how others have handled it. I did notice on our tour of homes last winter that almost every house with an HRV or even the fresh air in had a sagging intake line, the ones I could feel certainly had condensation and ice in-between the outer shell and flex duct where the insulation was. I asked about it in two of the homes and they said that was normal, in once case they had a regular metal duct obviously not insulated and was covered in ice, I just shook my head and walked out...

Yes ,the fresh air duct. The intake is a solid 6''duct with added exterior foil face insulation.
So what your saying is ad higher r-vallue to the duct insulation and problem solved?

Higher R value will indeed fix the problem, but it needs to be well air-sealed to keep humid room air from infiltrating in and coming in contact with cooler layers of the insulation. In a framing cavity this can often be pretty easy to do using rigid duct (with seams mastic-sealed) and blown insulation. Flex duct can be a pain to add air-tight insulation to.

R4 duct insulation may be OK for heating & AC ducts running within conditioned space, but it's woefully inadequate for ventilation air intakes. (Or even combustion air intakes for direct-vented appliances in cold/very-cold climates.)